Multiferroic LuFe2O4

Multiferroics are materials that exhibit more than one primary ferroic order parameter simultaneously (i.e. in a single phase). They have applications both in the bulk form (high-sensitivity ac magnetic field sensors and electrically tunable microwave devices) and as thin film (magnetoelectronic devices).

In the case of the mixed valence material LuFe2O4, the order parameters are ferromagnetism and ferroelectricity. It is a member of the RFe2O4 family where R are rare-earth elements. The crystal structure consists of the alternate stacking of triangular lattices of rare-earth elements, iron and oxygen.

FlatCone versus classical TAS

The sample was much smaller than usual and with a double twining (A and B). FlatCone made it possible to discover a third grain misoriented by about 90º. Thus only 1/3 of the sample volume contributed to the measured neutron scattering. All this would have made the alignment very difficult on a classical TAS instrument, with the additional problem of the attribution of satellites to A or B.

As demonstrated here by measurements on IN20, FlatCone provides a mapping of the scattering plane that makes things much easier and understandable.

Inelastic scattering

Nonetheless the above difficulties, FlatCone made it possible to observe an inelastic scattering. When the sample is heated, the magnon gap (> 5 meV) closes and fluctuations can be observed. A single night of measurements on IN20 was enough to obtain this result.

Ref: A.Boothroyd, D.McMorrow, H.Lewtas, J. Kulda, ILL Exp. report 4-01-689.